This invention pertains to a rotary cutting tool useful for remotely machining tube ends. It pertains particularly to such a rotary cutting tool device and method for remotely machining an exposed end portion of a tube, such as in preparation for welding on a replacement tube.
In remotely located tubes such as in steam generators for nuclear power plants, bundles of U-shaped heat exchanger tubes are usually provided which are welded into a relatively thick tube sheet of the heat exchanger. During operation of such steam generators over an extended period of time, such as 10 years or more, a corrosive sludge material forms and accumulates on the inner upper surface of the tube sheet. This accumulated sludge material causes corrosion of the heat exchanger tubes to an extent of potential or actual tube failure. To correct this serious problem without undesirable replacement of the heat exchanger, it is necessary to remove the old deteriorated tube end portions from the tube sheet and replace them with new tube portions which are remotely positioned and pressure-tightly welded into place, without removing and dismantling the entire heat exchanger assembly. However, because of the remote and relatively inaccessible location of the tubes and the radioactive environment which is usually involved, such tube replacement is very difficult to accomplish reliably and safely. Thus, a suitable solution to this problem has been needed, particularly for heat exchangers used in the nuclear power industry.
Many rotatable cutting tools are known in the prior art. For example, U.S. Pat. No. 3,051,059 to Davey discloses a tube end milling machine and U.S. Pat. No. 3,172,310 discloses a rotatable deburring tool, but they are not adapted to be remotely inserted through a tube. Also, U.S. Pat. No. 3,999,452 to Larson discloses a rotary device for chamfering the ends of a tube using dual cutting tools guided by the tube, but only the tool blades are inserted into the tube. Thus, the known prior art has not provided a rotatable cutting tool suitable for remote use for machining tube ends, such as in preparation for welding. However, the present invention advantageously provides a rotary cutting tool for remote operation which uses a central guiding member and multiple pivotable blades arranged to be extended radially outwardly, so that they contact both end and outer surfaces of a tube end for remotely machining the surfaces to a precise shape needed for subsequent welding to a mating replacement tube.